交流电是（）。A、电流的方向随时间变化而变化 B、电流的大小和方向都随时间变化而变化
题型：单项选择题
问题：
交流电是（）。
A、电流的方向随时间变化而变化
B、电流的大小和方向都随时间变化而变化
C、电流的大小和方向都随时间作周期性变化
D、电流的方向随时间作周期性变化
题型：单项选择题
For many employers, Facebook, MySpace and other social networking sites are already a threat （威胁） that cut into productivity．Now they have something else to worry about—the games hosted by these sites．
This new type of social gaming is called "asynchronous" gaming and allows people to play with their friends without having to be online at the same time．The low-intensity （低强度） engagement has made games such as FarmVille, Cafe World and Pet Society popular among employees who often log on during office hours．
"What we are seeing is that more and more people and organizations are recognizing the productivity lost so probably more chief information officers are blocking Facebook applications," Rebecca Wettemann of Nucleus Research said．
Boston-based Nucleus Research, which conducted a recent study into the effects of social networking sites on productivity, said nearly half of office employees in the United States access social networking sites at work, which leads to an average loss of 1．5 percent of total office productivity．
Facebook, which has 350 million users, says at least 20 percent of its members play games online．Sebastien de Halleux, CEO and co-founder of online game creator Playfish, said Asia is growing at a faster pace than other regions．"We had no idea that it would spread so fast．．．when we had 100,000 users after one month, we thought it was the biggest success ever．Now with 60 million users we think this is only the beginning of something much bigger," he added．
Zynga's FarmVille, the best known game with over 70 million active users to date, allows players to own a virtual farm where they can grow crops and raise animals．
While companies try to limit access to social networking sites, not everyone sees the games as harmful．
61．We can learn that Pet Society is a game _____．
A．popular among employers B．without having to be online
C．merely played during office hours D．that can be played online at a different time
62．It can be inferred from the passage that ____．
A．Playfish is owned by Sebastien and Rebecca
B．Playfish has over 70 million active users to date
C．Asia will be the largest potential market for Playfish
D．Playing online games loses 1．5 percent of total office productivity
63．The best title of the passage would be ____．
A．Social Network Gaming B．New Threat to Productivity
C．Social Networking Sites D．Latest Survey on Productivity
64．What would most probably be discussed next after the last paragraph?
A．Opinions in favor of online games．
B．Measures to limit access to social networking sites．
C．Suggestions on how to improve productivity．
D．More examples about the bad effects of online games．